• Mix the dough. Combine flour, salt, and yeast the bowl of a stand mixer fitted with a dough hook. In a separate bowl, whisk together warm milk, honey, egg, and vanilla. Pour the wet ingredients into the dry ingredients. Mix on low speed (KitchenAid speed 2-3) until the dough comes together in a shaggy messy ball on the dough hook, about 3-5 minutes. The dough will look dry at first, but will hydrate as it mixes. Be patient!
• Knead the dough. Increase speed to medium (KitchenAid speed 4) and knead until the dough passes the windowpane test, about 7-10 minutes. If the dough hasn't reached windowpane after about 7 minutes, drizzle in an additional ½ teaspoon milk while kneading, then cover and rest for 5-10 minutes. Knead 2-3 minutes more. It should get there!
• Add the butter 1 tablespoon at a time. With the mixer running on medium (KitchenAid speed 4), add the butter one tablespoon at a time. Let each piece fully incorporate before adding more. The dough will look like it is falling apart each time you add more butter, but it will come back together. Pause the mixer to gather the dough around the hook or scrape the butter down into the bowl occasionally as needed. This can take 10-15 minutes. Be patient!
• Knead the dough again. Increase speed to medium-high (KitchenAid speed 5-6) and knead until the dough is smooth, shiny, and passes the windowpane test again, about 5 minutes.
• Stretch out the dough. Plop the dough out on to a clean countertop. Press it flat with your hands, then gently stretch or roll the dough into a large square shape about 12 inches by 12 inches in size or bigger. Don't worry about it being perfect. Just stretch it out as best you can.
• Fold in the chocolate chips. Sprinkle about half the mini chocolate chips on the top half of the square of dough. Then fold the bottom half up to seal the mini chocolate chips inside. You'll now have one long rectangle. Sprinkle half remaining chips on the left half of the new clean dough surface. Fold the right side over to seal the mini chocolate chips inside, making a square of dough. Gently smush it down, then sprinkle the remaining mini chocolate chips over the new clean dough surface. Roll the dough up into a log or old all the corners into the center and pinch them together to seal the chocolate chips inside.
• Knead. Knead the dough briefly against the counter to help evenly distribute the mini chocolate chips inside and shape the dough into a ball.
• Cover and rise. Place the dough ball in a lightly greased bowl or container. Cover and let rise 1 hour at room temperature (72-75°F) until just about doubled in size. If not doubled after an hour, let it rise an additional 30-60 minutes until doubled. When you push a finger into it, the indentation should fill back slowly and incompletely.

Assembly and Shaping

• Deflate the dough. Turn dough out onto a clean, lightly floured work surface. Use your hands to gently deflate the dough.
• Shape the brioche loaf. Stretch or roll the dough into a rectangle about an inch thick. One side of it should be about 9 inches long, the same length as your loaf pan. Fold the two sides in an inch or two as needed to get straight edges, then gently roll the dough up into a log. Place it in a greased 9x5" loaf pan. It may not fill out the pan just yet, that's okay.
• Final Rise. Cover and let rise at room temperature for 1-2 hours or until the dough has almost filled out the pan. When you press a finger into the dough it should feel soft, springy, and airy and the indentation should fill back in slowly but not completely.

Baking

• Towards the end of the dough rising, preheat the oven to 350°F. Whisk together egg, milk, and salt to make the egg wash.
• Egg wash. Brush the top of the dough with egg wash. Then bake for 40-45 minutes until deeply dark golden brown on top and an internal temperature of 190°F. Check the loaf after 30 minutes; If the top appears to be browning too much, tent a sheet of aluminum foil over the top.
• Cool. Let cool slightly in the pan, then remove to a rack to finish cooling completely.